The present invention relates to a system for detecting slippage of a clutch for an internal combustion engine and for preventing the breakdown of the clutch caused by the resulting overheating.
A clutch such as a friction clutch or an electromagnetic clutch provides slippage between a drive member and a driven member, when the speed of the crankshaft of the engine is different from the speed of a driven shaft. This slippage generates heat which elevates the temperature of the clutch. In normal clutch operation, the amount of heat generated is negligible, but if the slippage continues for a considerable time, overheating can occur which may cause clutch elements to become inoperative.
For example with respect to an electromagnetic clutch, the latter is arranged so that the clutch torque is controlled in dependency on the engine speed to allow smooth starting of the vehicle, even in starting on a steep uphill. Slippage in the clutch provides a clutch torque suitable for the starting. However, if such slippage continues too long, the clutch will be overheated causing deterioration of the clutch operation. In order to prevent this condition from occurring a sensor for detecting clutch temperature is provided in some conventional electromagnetic clutches. Such a detecting system is disclosed in Japanese patent application laid open No. 56-60733, nevertheless it is difficult to directly detect the temperature of a heat generating portion of a clutch, because such a portion is typically sealed in the clutch.
Consequently, heat detecting sensors are usually provided for detecting the temperature of a clutch outer member such as a housing. Using such a sensor, rapid elevation of the temperature caused by continuous slippage cannot be immediately detected, a breakdown of the clutch may result before the overheating condition is detected.